The present invention relates to cationic dyeing of cross-linked phenolic resin fibers and blends thereof with aromatic polyamides.
Novoloids, infusible cured phenolic resins containing at least 85 percent cross-linked novolac, may be produced by fiberization of a novolac melt and subsequent cross-linking or curing to an infusible stage. Curing may be effected in the presence of a source of methylene groups, such as paraformaldehyde, formaldehyde, or hexamethylenetetramine, and preferably also in the presence of an acidic or basic catalyst. Such novoloid fibers are disclosed in the following U.S. Patents, which are incorporated herein by reference: U.S. Pat. No. 3,650,102, issued Mar. 21, 1972, to Economy et al; U.S. Pat. No. 3,716,521, issued Feb. 13, 1973, to Economy et al; and U.S. Pat. No. 3,723,588, issued Mar. 27, 1973, to Economy et al. Novoloid fibers may be formed into felts, mats, cloths, rovings, or other useful embodiments in accordance with conventional fiber handling techniques. A fabric of such fibers is disclosed by U.S. Pat. No. 3,628,995, issued Dec. 21, 1971, to Economy et al.
Novoloid fibers have a number of highly desirable attributes which render them of value in numerous applications. Their most outstanding virtue is excellent flame resistance. When subjected to flame, the infusible fibers do not melt, but rather char to produce carbon fibers, which continue to retain the shape and approximate dimensions of the original fibers, and which continue to afford extremely effective protection from flames. Accordingly, the fibers are of great utility in the fabrication of flame-protective clothing, as well as drapes, carpeting, upholstery, and the like which are especially suited for use in areas where fire constitutes a particular hazard. Such fibers also provide very effective thermal and accoustical insulation, and again are particularly useful for these applications where fire is a hazard. The fibers have suitable mechanical properties, such as tenacity and break elongation, to permit their being processed into yarns, woven and knitted fabrics and the like, as well as various non-woven forms such as felt, batting, and paper..
Notwithstanding such desirable attributes, infusible cured phenolic resin fibers have several disadvantages. Just after curing, they are generally quite intensely colored, the hue ranging from very pale yellow to gold. Moreover, upon standing, the coloration may increase considerably in intensity, becoming deep brown or reddish brown. Thus, the fibers are known to possess rather poor color fastness.
Such novoloid fibers are particularly resistant to normal commercial dyeing processes. Accordingly, it has been difficult to obtain fibers and/or fabrics of the desired range of colors and color fastness. This detriment has a marked effect upon their acceptance by the textile industry and by the consumer with respect to applications for such fibers and fabrics in which color is an important factor.
In an attempt to overcome the deep coloration of such fibers, esterification or etherification of the phenolic hydroxyl groups may be utilized. In accordance with U.S. Pat. No. 3,716,521, of Economy et al, infusible cured phenolic resin fibers may be reacted with any of a wide variety of suitable esterification or etherification reagents, at a suitable temperature, for sufficient time to block at least about 50 percent, and preferably about 90 percent, of the phenolic hydroxyl groups of the cured resin. The blocking of phenolic hydroxyl groups may be accomplished after the resin has been cured to the point of infusibility, notwithstanding the cross-linked nature of the resin. Such fibers, while generally white in color and quite colorfast, have also, in the past, been difficult to dye to desired shades using commercially acceptable dyeing processes.
Cationic, or basic, dyes have been successfully utilized for dyeing such acrylic fibers as Orlon (E. I. duPont de Nemours and Company), Creslan (American Cyanamid Company), Acrilan (The Chemstrand Corporation), and polyester fibers such as basic dyeable Dacron (E. I. duPont de Nemours and Company). The basic nature of this family of dyes is due to one or more amino or imino groups. Typical chemical structures found in cationic dyes include azines, thiazines, xanthenes, diarylketonimines, triarylmethanes, and polymethines. While cationic dyes exhibit generally good fastness to light and washing when dyed on acrylic fibers, they have not been successfully used for dyeing phenolic fibers, and novoloid fibers in particular, prior to the present invention.